This invention relates generally to factory automation equipment and more specifically to material distribution systems.
Automating material transfer between machines and storage areas in a factory is a very mature field, and hundreds of patents and known methods exist. Examples of known methods include conveyors, guided vehicles, rail-based systems and autonomous vehicles. However, virtually all these approaches either fall short in flexibility or cost too much. Furthermore, most flexible or semi-flexible systems evolved for the automotive industry, and thus they are designed to carry heavy loads so they are mechanically complex. In price-sensitive applications, therefore, batch processing with hard automation, such as transfer lines, or humans carrying containers has been the norm. However, with lot sizes decreasing as customer demand for customization increases, there exists a need for a very low cost, flexible and reliable material transport system for factory automation.
As an example of a system currently used in semiconductor manufacture, PRI Automation, in Billerica Mass., has been basing an automation system on U.S. Pat. No. 4,926,753 xe2x80x9cFlexible material transport systemxe2x80x9d and subsequent related patents such as U.S. Pat. No. 5,673,804 xe2x80x9cHoist system having triangular tension membersxe2x80x9d. Competitors, such as Murata and Daifuku in Japan, have similar systems in that they are also based on a track with a robotic car that has two sets of wheel systems, or bogies as they are known in railroad terms. In effect these companies have miniaturized well-known railroad solutions; however, this adds a great deal of complexity and cost just in terms of the number of parts.
For the manufacture of parts on silicon wafers, the so-called front-end of semiconductor manufacturing, the high cost was justifiable. For the so-called back-end, which involves packaging and testing the devices, the product density is much lower, and the allowable costs are also much lower; hence such systems have not been justifiable, and most work is still done by people transporting materials. It is interesting to note that railroads are designed with a set of functional requirements that emphasize stability when the load is carried on top of the car, and this seems to have driven the development of automation for the front end. Even systems, such as sold by Murata, that carry the load beneath the car still use the double bogie railroad car design. Perhaps this is so because these systems are also often sold in a scaled-up mode for large load capacity systems that need pitch resistance.
In some systems, the load hangs below the cart. However, such systems have not generally been used in factory automation equipment, with such systems more likely to be used in aerial tramways and meat packing plants. In these cases, the payload is carried by structure that is mounted to a carriage with a pivot mount, which is called a xe2x80x9cbeef trolleyxe2x80x9d. This eliminates the need for two independent wheel carriage systems, which greatly reduces cost and complexity. A beef trolley, however, is not motorized, but is moved along by contact with a chain, or it is pulled manually. In addition, the use of only one wheel results in substantial swinging.
With the foregoing background in mind, it is an object of the invention to provide a system for transferring materials between machines and storage systems.
The foregoing and other objects are achieved in a material transport system having a track with carts riding on the track. Material is carried on each cart. In one embodiment, the carts have one or more wheels that engage the track and the track and the wheels are shaped to provide limited points of contact between the wheels and the track, thereby providing a marginally over-constrained system that is stable.
In other embodiments, the carts are balanced to hang on the track, with the load suspended below the cart. In certain embodiments, the balance is enhanced by a gyro-stabilizer in the cart.
In the preferred embodiment, each of the carts is motorized and can move rapidly around a track that has bends and inclines to allow three dimensional motion of the cart.